Reporting from Washington and Moscow — The Russian leader on Thursday accused Secretary of State Hillary Rodham Clinton of inciting protests against his country's troubled parliamentary elections, an unusual personal attack suggesting that one of the Obama administration's main foreign policy initiatives is unraveling.

Warning that Russia needs to crack down on "interference" by foreign governments, Prime Minister Vladimir Putin complained that Clinton had denounced Sunday's elections as fraudulent before she had reliable information. He said her criticism had mobilized his political opponents.

"She set the tone for some activists in our country and gave them a signal," Putin said in televised remarks. He added that the U.S. is seeking to influence Russian politics with the aim of weakening a rival nuclear power.

Putin long has been wary of U.S. efforts to promote democracy and human rights, and he delivered his harsh comments as he launched his campaign for Russia's presidential election in March. He is expected to win back the job he left four years ago because of term limits, but may have a harder time after his United Russia party suffered an unexpected setback in the parliamentary balloting.

Although Putin has served as prime minister for the last four years under his protege President Dmitry Medvedev, Putin has been widely regarded throughout that period as the most powerful man in Russia.

His outburst is the latest sign that President Obama's much-publicized effort to "reset" relations with Russia, which his aides have portrayed as one of his most important foreign policy achievements, is in trouble, said analysts in both capitals.

"Russian-American relations are like driving a bicycle," said Andrei Kortunov, president of the New Eurasia think tank in Moscow. "The slower the speed, the more chances to fall."

Washington and Moscow are in a bitter standoff over the North Atlantic Treaty Organization's planned missile defense system in Eastern Europe. The long-standing deadlock appears to worsen last month when Medvedev threatened to deploy nuclear missiles close to Europe's border to target NATO missile defense installations.

On Dec. 1, Medvedev announced that he had put a new early-warning radar system on combat alert. The NATO missile defense system, he said, "causes significant problems" for Russian security.

The United States and Russia also have clashed all year over sanctions against Iran, the crackdown on protests in Syria, the NATO-led air war in Libya, the Arab-Israeli peace process and other concerns.

A downturn in relations could set back several U.S. diplomatic priorities, starting with the effort to halt Iran's suspected nuclear weapons program.

Clinton criticized the Russian elections several times this week. She said Monday that Russians "deserve the right to have their voices heard and their votes counted." On Thursday, when asked about Putin's comments, she replied that U.S. concerns "were well founded about the conduct of the election."

The Kremlin fired back repeatedly, denouncing U.S. complaints as "hostile" and urging American officials to clean up U.S. elections.

Russian authorities moved forcefully to rein in protests that followed reports of ballot stuffing and other fraud, arresting hundreds of demonstrators.

Andrew Kuchins, a Russia specialist at the Center for Strategic and International Studies, a Washington-based think tank, said a further crackdown on pro-democracy groups would be "potentially explosive" because the Obama administration probably would respond strongly.

"If the regime really comes down hard, then all bets are off," he said.

James Collins, a former U.S. ambassador to Russia who was in Moscow last week, said he believed Clinton's criticism was unnecessary because international observers already had exposed ballot stuffing and other polling problems.

"I don't see why we have to be out front," he said. "It just makes it easy for Putin to say that outsiders are interfering."

Relations between Washington and Moscow were badly strained when Obama took office. They reached a high point last year when the two nations signed a strategic nuclear weapons deal and agreed to expand civil nuclear energy in Russia.

Moscow also agreed to allow NATO to carry supplies through Russia for the war in Afghanistan, and threw its support behind United Nations sanctions last year that were aimed at halting Iran's nuclear program. Both those initiatives are now in doubt.

In addition to the dispute over missile defense, Putin and Medvedev have denounced what they view as U.S. duplicity in seeking Russian support at the U.N. for NATO intervention to protect civilians caught in Libya's civil war last spring. The Russian leaders complained that Washington and its allies used the air war to help rebel forces oust dictator Moammar Kadafi.

"We're not seeking a positive or happy-to-good relationship with Russia," a senior administration official said. "We're seeking to work with Russia on outcomes that advance our interest.... We all need to be a little realistic about our expectations of what Russia will do and not do with us."